There are ALL sorts of things to buy for your ship, and when you buy the basic items, you get more advanced versions. Plus there are some purely cosmetic things to do to your ship, too! All upgrades are paid for in raritanium. Don't obsess too much about raritanium, you can easily get as much as you could possibly want, and will soon have all the upgrades possible plus be able to change your ship's color every 5 minutes if you want to.